1. Field of the Invention
The present invention relates to a digital/analog converting apparatus applied to a spatial optical modulator (hereinafter, referred to as an “SOM”), and more particularly, to a high resolution digital/analog converting apparatus implemented to provide higher resolution than that obtained using a DAC (for example, an 8-bit DAC) with low resolution, to significantly reduce a size of SOM IC and to be operated at relatively high speed when operating multi-channels.
2. Description of the Related Art
Generally, a spatial optical modulator (SOM) driver IC is used to drive an SOM device. In developing the SOM driver IC, a conventional similar IC, as shown in FIG. 1, outputs a single voltage from a desired gray scale using an 8-bit resolution DAC.
A conventional 8-bit digital/analog converting apparatus will be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic view illustrating the conventional 8-bit digital-analog converting apparatus. As shown in FIG. 1, the conventional 8-bit digital/analog converting apparatus includes a resistor string 10 having a plurality of resistors R0 to R256 connected to each other in series between two terminals of operating voltages Vd1 and Vd2 and dividing the operating voltages Vd1 and Vd2 using the plural resistors R0 to R256, a decoder 20 to control a DA conversion of converting an 8-bit digital signal into a corresponding analog signal, and a switch unit 30 to select a voltage from voltages VR<0> to VR<256> divided by the resistor string 10 according to a control of the decoder 20.
The decoder 20 includes a first decoder 21 to control a DA conversion of converting a high 4-bit digital signal among 8-bit signals into a corresponding analog signal, and a second decoder 22 to control a DA conversion of converting a lower 4-bit digital signal among the 8-bit digital signals into a corresponding analog signal.
The 8-bit DA converting switch unit 30 includes a voltage group selecting unit 31 to select a single voltage group from a plurality of voltage groups respectively including a predetermined number of voltages divided by the resistor string 10, and a voltage selector 32 to select a single voltage Vout from the voltage group selected by the voltage group selecting unit 31 according to the control of the second decoder 22.
The voltage group selecting unit 31 includes a plurality of group switches GS1 to GS16 to select all of voltages included in the voltage group selected from the plural voltage groups according to the control of the first decoder 21. The voltage selector 32 includes a plurality of switches SW1 to SW16 commonly connected to respective corresponding positions of the plural group switches GS1 to GS16, and selects a single voltage Vout from the selected voltage group by which one of the plural switches SW1 to SW16 is turned on.
FIG. 2 is a schematic view illustrating the 8-bit DA converting switch unit in FIG. 1.
Referring to FIG. 2, the 8-bit DA converting switch unit 30 includes the plural group switches GS1 to GS16, and the plural group switches GS1 to GS16 each respectively include sixteen (16) switches, namely, SW1 to SW16, . . . , SW209 to SW224, SW225 to SW240, and SW241 to SW256.
In the conventional digital/analog converting apparatus, if the voltage group selecting unit 31 includes sixteen group switches and the voltage selector 32 includes sixteen switches, since one of 256 voltages can be selected by the 256 switches, the 8-bit (28=256) DAC is implemented.
When an apparatus higher than the 8-bit digital/analog converting apparatus, namely, a 10-bit digital/analog converting apparatus is implemented using an apparatus such as the conventional 8-bit digital/analog converting apparatus, the 10-bit digital/analog converting apparatus must include four times the number of the resistors and switches of the conventional 8-bit digital/analog converting apparatus. For this reason, the size of the SOM IC using the converting digital/analog converting apparatus is significantly increased so that the conventional digital/analog converting apparatus cannot be used in an SOM IC having a limit in size. Moreover, it is difficult to implement electric circuits and the electric circuits are complicated. Thus, the manufacturing costs of the SOM IC increase.
Further, when the 10-bit digital/analog converting apparatus using the conventional digital/analog converting apparatus, as described above, since the size of the 10-bit digital/analog converting apparatus becomes four times that of the conventional 8-bit digital/analog converting apparatus, the yield thereof is deteriorated. Moreover, since an area of the SOM IC is increased, parasitic components of the SOM IC are increased, and as a result, it is more difficult to guarantee desired superior performance of the SOM IC.
In other words, if a driver IC having 10-bits (1024 level) is implemented using the conventional digital/analog converting apparatus, the number of the resistors used in the resistor string must be a total of 1025 and the number of the switches used in the switch unit 30 becomes 1024. According to this fact, although the total number of the resistors 258 and the total number of the switches is 256 in the conventional 8-bit digital/analog converting apparatus, in the 10-bit digital/analog converting apparatus, the numbers of the resistors and the switches must be increased by four times so that the size of the SOM IC using the 10-bit digital/analog converting apparatus is significantly increased.
Additionally, when the size of the IC chip is increased by four times, the number of the ICs produced from a single wafer is reduced so that the productivity of the IC chip is deteriorated and the manufacturing costs thereof increase.